My mom told me that when I was young, and was questioning why have kids. Her viewpoint, paraphrased loosely, was that people who don't have kids are not forced to undergo the dramatic self-sacrifices that parents are, and aren't forced to nurture and care for another human 24/7 whether they feel like it at the moment or not. They are never have that transformational washing over of incredible torrents of love for a helpless being, which immediately calls for putting oneself as a lower priority and another person as the highest priority. Therefore, they don't mature as much, and always will put their own needs first.
What I don't really understand is why it's so important for one person to subordinate themselves to another. After all, having children doesn't make parents into great philanthropists ready to sacrifice themselves for the greater good - just into people who make sacrifices for their offspring, in whom they have a vested interest. There's nothing particularly selfless about that sort of self-sacrifice.
What's wrong with putting your needs first, provided that doing so hurts no-one else? Why must 'maturity' equal self-effacement? This sort of idea is constantly repeated without question, but I don't really get it.